THURSDAY, May 8, 2014 (HealthDay News) -- Zontivity (vorapaxar) tablets have been approved by the U.S. and Drug Administration for people at high risk of heart attack or stroke.

The drug is the first in a new class called protease-activated receptor-1 antagonists, designed to weaken the tendency of platelets to clump and form a blood clot. But the agency said the drug increases users' risks of developing life-threatening bleeding. Zontivity's label includes a boxed warning describing this risk, the FDA said Thursday in a news release.

The drug is meant for people who have had a previous heart attack or blocked arteries in the arms or legs. It should not be used by people who have had a prior stroke, "mini-stroke" or a prior episode of bleeding in the head, the agency warned.

The most common side effects include bleeding and bruising. Users who have these side effects should report them immediately to their doctors, the FDA advised.

Zontivity is made by Merck Sharp and Dohme Corp., whose parent Merck & Co. is based in Whitehouse Station, N.J.